Revealing mistake: In this episode's present-day 1963, the scientists view film footage said to have been taken "yesterday." But the rather obvious crowd scene stock footage is ten years old, featuring cars and clothing no newer than 1953.

Revealing mistake: When the alien posing as a human is exposed, the OBIT screen shows his "true" alien form while he continues to appear human to the naked eye. The actor in alien costume on the screen copies Jeff Corey's movements, but at one point rather badly shatters the illusion by forgetting to raise his arms when Corey does.

Revealing mistake: The injured Spain falls and tries to crawl away from the alien, leaving handprints in the dust on the floor. Just to his left, you can see several handprints already on the floor from previous takes.

When Dr. Stone's assistant helps him up from the floor, there's a lopsided, circular diagram drawn on the chalkboard behind them. One shot later, the diagram has changed into a perfectly round circle and has moved itself several inches higher on the board.

This is the only Outer Limits episode that lacks both opening and closing narration. It was absent because "Forms" was the unsold pilot for a series called The Unknown. A second version, stripped of all its supernatural elements (Tone was simply a mad scientist, not a real time traveler), also failed to sell.